Process for crystallizing sugar from solution



G. ASSALlNl Jan. 22, 1963 PROCESS FOR CRYSTALLIZING SUGAR FROM SOLUTION Filed April 15, 1960 Centrifuge 3,074,819 PRGCESS FQR CRYSTALUZENG SUGAR FROM SOLUTEGN Giuseppe Assalini, Genoa, Italy, assiguor to Rohrn &

Haas Company, Philadeiphia, Pa, a corporation of Delaware Filed Apr. 13, 1960. Ser. No. 22,ii55 11 Claims. (Cl. 12746) This invention relates to an improvement in processes for manufacturing sugar. More particularly, it has reference to a method for producing sugars and edible sirups from sugar-bearing sources such as sugar cane and beets, fruit juices, corn products, and liquid molasses products including those products which otherwise would not be suitable for human consumption.

A principal application of the invention is in the crystallization of sugar. Of especial importance is the application to the crystallization from sugar juices having extraneous substances which form organic complexes with sugar, or which cause the liquid to have such a viscosity and density that crystal formation is inhibited or prevented altogether. By sugar juices is meant, in particular, the molasses-like substances which have been exhausted with respect to the crystallization of sugar by conventional means. The term, as hereinafter used throughout the specification and claims, will be understood to encompass those juices from which the sucrose otherwise is in condition to be crystallized by conventional processes except for the fact that crystallization was prevented because of the presence of the extraneous substances or impurities mentioned above.

In essence, the present invention is characterized by the fact that high molecular weight, oil-soluble, water insoluble, liquid organic amines which have ion exchanging properties are used. These liquid ion exchangers simultaneously lower the viscosity and form organic complexes with the non-sugars present in molasses and other juices, the sugar-containing liquid being free to crystallize as it thus becomes more movable and free from the impurities. The liquid exchangers may be used as such, but generally may be preferred to be used in some desired dilution with a hydrocarbon or higher alcohol.

My novel process is so effective that it makes possible the obtainment of sugar even after sugar can no longer be economically recovered by conventional crystallization processes such as are described in McGinnis, Beet-Sugar Technology (Rheinhold, New York City, 1951), at pages 136-438, and Spencer-Meade, A Handbook for Cane- Sugars Manufacturers and Their Chemists (Wiley, New York City, 1929), at pages 86-98. Moreover, the process is as simple to operate as it is effective in its results; and its results amount to quite an improvement over the prior art.

Although the process will readily be understood to have many modes of practical, commercial scale utiliza tion, to illustrate it reference may be made to the annexed schematic diagram of a simplified plant and apparatus for implementing the novel method. As there shown, a suitable liquid anion exchanger is introduced via piping 1, while the sugar-bearing juices are introduced through piping 2, both into an appropriate massecuite mixer 3. An electric or other comparable motor 4, together with a gear reducer 5, serve to turn the helically-shaped blades 6 in mixer 3 at a uniformly slow speed. The mixture of sugar juices and the liquid ion exchanger are mixed for the desired length of time and at optimum temperature conditions to enable the exchanger to take the impurities out of the juices. The mixture is then caused to pass out of the mixer through piping 7, valve 8, piping 9, and into centrifuge 10.

In the centrifuge the newly formed crystals of sugar are separated from the liquid ion exchangers, which by this time have taken on the non-sugars by forming complexes therewith. The sugar crystals drop out of the centrifuge through valve 11 and piping 12 onto a movable belt carrier 13 which transports the crystals to a point where they can be removed conveniently. The solution of liquid ion exchangers and the non-sugars is removed from the centrifuge through piping 14 and thereby conveyed to a device (not shown) for separately recovering the non-sugars and regenerating the ion-exchangers for further use.

The process of the present invention is a significant improvement over such prior art techniques as that known as crystallization in motion which was first used in the European beet-industry, and which is described on pages 97-98 above-mentioned Spencer-Meade book as follows:

This process consists essentially in keeping the crystals of a massecuite in motion while completing the crystallization. The best results are therefore obtained in pushing the crystallization so far as it practicable in the vacuumpan and completing it in the crystallizer.

A theory of the process that conforms with general experience with cane-sugar is as follows: If the crystals of a massecuite be kept constantly in motion and be brought intimately in contact with the sugar still in solution, this sugar will deposit upon the crystals already present rather than form new ones, provided there is no sudden reduction of temperature to increase the super-saturation. Manifestly it is impossible to produce a stirring device that will move each crystal independently, in the heavy viscous massecuite, to entirely new environment, so that it may be brought into contact with fresh portions of the sugar in supersaturated solution. Further, there is little possible freedom of motion for a crystal in a dense massecuite, since the film of molasses separating it from its neighbors is but a few thousandths of an inch in thickness. The crystal gradually takes on the sugar in its own immediate neighborhood, reducing the density and viscosity of the molasses surrounding it, and in its increase of size it approaches nearer a fresh source of sugar. Great inequality of density cannot long exist, since the stronger solutions near by must mix with the weakened solution by diffusion. The motion of the stirrers of the crystallizer, by rocking the crystals, promotes this diffusion and a uniform fall of temperature in the massecuite. With the fall of temperature, the saturation of the solution resulting from the growth of the crystals is changed to supersaturation and crystallization continues. A point is finally reached When the crystal size ceases to increase. This is due to the viscosity of the medium and not to lack of a supersaturated solution of sugar. When this point is reached, the massecuitle should be diluted with water or if preferred with dilute molasses. Diffusion is again possible and the crystallization again progresses. The dilution must be repeated from time to time for the best results. Water is preferable to molasses as a diluent since it does not add solids to the massecuite.

In the present invention, the liquid ion exchangers not only serve to dilute the viscous sugar juices and thereby increase the mobility thereof, but actually remove the non-sugars which are the major cause of the fluids excessive viscosity. The organic complexes formed by the liquid exchangers and the non-sugars separate out into an organic phase which is distinct from the phase consisting of an aqueous solution of the sugar juices. This makes separation by centrifuging, as described above, and removal of the non-sugars a relatively simple matter. Crystallization of sugar is thus promoted with far greater efficiency than ever before, without the need for the numerous re-dilution and recrystallization procedures which featured the prior art crystallization in motion process.

-Either' product may be any composition in which R is an alkyl group in the C to C range, but generally it consists of a mixture of compositions whose average carbon content falls within that range.

The many liquid-ion exchangers which maybe used form a broad class comprising a mixture of amines con sisting principally of t-C l-l NHX where n 'is a numher from 11 to 24 ar'1d X is H, or an alkyl or an alkenyl group of no more than 14 carbon atoms. The amines may be primary, secondary, tertiary, and even quaternary ammonium compounds, each compound having a molecular weight of at least about 185. Compositions (1) and (2) above are representative of the primary amines. Typical of the secondary amines which could be employed are dodecylbenzyl t-dodecylamine and dodecenyl t-dodecylamine. Typical tertiary amines are tridodecenyl and dodecylbenzyl-di-n-butyl amines. Representative of the quaternary ammonium compounds are dodecenyl trimethyl ammonium chloride and poly(metamethylparadodecyloenzyl) dimethyl 'y (acrylamido) propylammoninum chloride.

The liquid exchangers may be used in their concentrated-form. However, it is often preferred to dilute them with a hydrocarbon solvent or a higher alcohol. 7 Examples of such diluents are kerosene, benzene, tri-decyl alcohol, etc. Many other diluents are available, the main requirement being that they should be relatively water-immiscible and, of course, inert in the reaction.

Example 1 Four hundred cc. of sugar juices having'the' viscous consistency of thick molasses at a temperature of 25 C. was placed into a'mixer such as 3 in the attached drawing. The juice had an analysis ofBrix 83; sugar, 50.60; and purity, 60.96. One cc. of the liquid ion exchanger whose structural formula is identified as (1) above was added to the juice in the mixer, and the mixer was made to revolve at a speed of one r.p.m. for five hours. At the end of this time the mixture was drained through pipes 7 and9, passing through valve 8, into centrifuge 10. The mixture was centrifuged for 20 minutes, during which time the non-sugars complexed with the liquid ion exchangers and were allowed to exit through pipe 14. Thereafter, valve 11 was opened and the sugar solids were permitted to fall from the centrifuge through valve 11 and pipe 12 onto the'movable conveyor 13 which transported the crystalline sugar to be dried at another point.

Examination of the crystals under the microscope'indicates that they were all substatnially pure crystals of sugar. Further testing of the sugar crystals showed virtually none of the original non-sugar impurities remaining therein.

Example 2 Example 1 was repeated except that two cc. of the liquid ion exchanger were used this time. Again, sugar crystals Were obtained.

' Example 3 Example 1 was repeated except that instead of using the liquid ion exchanger identified as (1) above the one' identified as (2) above was used and sugar crystals were obtained as before.

Example 4 Example 2 was repeated except that'instead of using the liquid ion exchanger identified as (1) above the one identified as (2) above was used and sugar crystals were obtained as before.

Example 5 Example 1 was repeated except that the time the mixer was reduced to two hours. An equivalent quantity of sugar crystals was obtained, notwithstanding" the redut'cion of time. 7

Example 6 Example 2 was repeated except that the time in the mixer was reduced to two hours. An equivalent quantityof sugar crystals was obtained notwithstanding the reduction of time.

Example 7 Example S-Was repeated except that the time in the mixer wasfurther reduced to 20 minutes. Again a substantially equivalent quantity of sugar crystals was obtained notwithstanding the further reduction of time.

Example 8 Example '6 was repeated except that the time in the mixer was further reduced to 20 minutes. Again a substantially equivalent -quantity of sugar crystals was obtained notwithstanding the further reduction of time.

It will be apparent from the foregoing thatnumerous variations in techniques may be employed without deviating from'the spirit or scope of this invention. Times of mixing, temperature, amounts'of the liquid ion exchanger employed, and other such factors can be varied to get maximum results'with just a little more or'less routine experimentation.

I claim:

1. 'A' process for crystallizing sugar from impure sugar juices which comprises mixing together with an aqueous solution of the juices a high molecular weight, oil-soluble, water-insoluble, liquid organic amine having anion exchanging properties fora length of'time which is sufii- -cient to have some of the non-sugars present in the juices form organic complexes with the amine, centrifuging the mixture so as to separate the phase containing the organic am ne and complexes from the phase containing the aqueous sugar juices'which, because of theirmore purified state, commence the formation of sugarcrystals, then drawing off the crystallized sugar.

m 2. The process of claim lin which the liquid ion exchanger is a mixture of amines having the formula t-c l-I p NHX where n is a number from 11 to 24 and X'is a member of the class consisting of H, an alkyl "group of no more than 14 carbon atoms, and an allcenyl group of no more than 14 carbon atoms.

3. The process of claim 1 in which the amine is selected from the class consisting of 5. The process of claim 3 1i-24 2a 49 2) u a- 6. The process of claim 3 dodecylbenzyl t-dodecylamine.

7. The process of claim 3 dodecenyl t-dodecylamine.

8. The process of claim- 3 tridodecenyl amine.

9. The process of claim 3 dodecylbenzyl-di-n-butyl amine.

which the 6 amine is 10. The process of claim 3 in which the amine is dodecenyl trimethyl ammonium chloride. amine is 11. The process of claim 3 in which the amine is poly(metamethylparadodecylbenzyl) dimethyl "y (acrylamine is 5 amido)propylammonium chloride.

References Cited in the file of this patent amine is UNITED STATES PATENTS mine is 10 2,391,843 Rawlings Dec. 25, 1945 2,563,006 Collier Aug. 7, 1951 

1. A PROCESS FOR CRYSTALLIZING SUGAR FROM IMPURE SUGAR JUICES WHICH COMPRISES MIXING TOGETHER WITH AN AQUEOUS SOLUTION OF JUICES A HIGH MOLECULAR WEIGHT, OIL-SOLUBLE, WATER-INSOLUBLE, LIQUID ORGANIC AMINE HAVING ANION EXCHANGING PROPERTIES FOR A LENGTH OF TIME WHICH IS SUFFICIENT TO HAVE SOME OF THE NON-SUGARS PRESENT IN THE JUICES FORM ORGANIC COMPLEXES WITH THE AMINE, CERTRIFUGING THE MIXTURE SO AS TO SEPARATE THE PHASE CONTAINING THE ORGANIC AMINE AND COMPLEXES FROM THE PHASE CONTAINING THE AQUEOUS SUGAR JUICES WHICH, BECAUSE OF THEIR MORE PURIFIED STATE, COMMENCE THE FORMATION OF SUGAR CRYSTALS, THEN DRAWING OFF THE CRYSTALLIZED SUGAR. 